The fifth major version of Apple’s mobile operating system adds over 200 new features, including Notification Center, iMessage and Newsstand. Furthermore, the software update adds support for Apple’s iCloud service, which was also announced today.

The key features Apple outlined are:

Notifications

iMessage

Reminders

Twitter integration

Newsstand

Improved Camera app

Improved Safari app

Improved Mail app

PC-free

Photo editing

According to Apple, iOS 5 is compatible with the iPhone 3GS, iPhone 4, the third and fourth generation iPod touch devices, the original iPad and the iPad 2. (And, of course, Apple’s new iPhone!)